The present invention relates to a lower vehicle-body structure of a vehicle, in which arm members constituting a suspension are supported at a sub frame at a front portion of a vehicle body of an automotive vehicle, for example.
Conventionally, a lower vehicle-body structure of a vehicle, in which a crush space to absorb a collision impact in a vehicle frontal collision is provided at a front portion of a vehicle body, is known. Specifically, this kind of lower vehicle-body structure comprises a pair of front side frames extending in a longitudinal direction at both sides of the front portion of the vehicle body. The front side frames are configured to easily have a buckling deformation receiving an impact load caused by the vehicle frontal collision, so that the collision impact in the vehicle frontal collision can be absorbed properly. The crush space is a space to absorb the collision impact though the buckling deformation of the front side frames. Thus, ensuring the crush space to absorb the collision impact sufficiently can prevent the impact load from being transmitted to a vehicle rear.
In the above-described structure, a power train, such as engine, and the sub frame comprising a suspension cross member are arranged in the above-described crush space. The suspension cross member supports a suspension member which is arranged right below or in back of the power train. Further, the power train and the sub frame are supported or fixed to interconnect both sides of the crush space in a vehicle width direction.
Since the power train and the like interconnect both sides of the crush space in the vehicle width direction as described above, the front side frames may be restrained from deforming in the vehicle width direction against the impact load from the vehicle front, so that the sufficient buckling deformation may not be obtained. Thereby, there is a concern that the crush space to absorb the collision impact sufficiently may not be secured.
Therefore, some technologies to secure the crush space by separating the power train or the sub frame off the vehicle body in the vehicle frontal collision have been proposed.
Specifically, some weak portion is provided at a connection portion of the sub frame to the vehicle body, and the sub frame is separated off the vehicle body by this weak portion in the vehicle frontal collision, so that the crush space to absorb the collision impact sufficiently can be secured (see Japanese Patent Laid-Open Publication No. 2004-148960).
Meanwhile, a structure in which arm members constituting the suspension, such as lower arms, are swingably supported at the sub frame is known as one of the lower vehicle-body structures at the front portion of the vehicle body.
In this kind of structure, it may be considered, in order to provide effects of reducing the road noise during the vehicle traveling, that the attachment rigidity of the support portion at the rear portion of the arm members is improved by supporting rear portions of the arm members at both the sub frame and the front side frames.
However, there is a concern that this supporting of the rear portions of the arm members at both the sub frame and the front side frames may prevent a smooth separation of the sub frame together with the arm members in the vehicle frontal collision. Thus, there may be a possibility that the crush space to absorb the collision impact sufficiently is not secured.